1. Field of the Invention
The present invention relates to an image forming apparatus which transfers a toner image carried by an image carrier to a recording material using an electrophotographic technique for a copying machine or a laser printer and, in particular, to an image forming apparatus including a transfer belt which performs the transfer to a recording material and the conveyance thereof.
2. Description of the Related Art
In an electrophotographic apparatus in which a recording material is carried and conveyed by a transfer belt stretched by a plurality of rollers, the recording material on the transfer belt passes a transfer nip portion and is electrostatically sucked on the transfer belt.
If the stiffness of the recording material is weak, the recording material cannot be separated from the transfer belt by merely using the curvature of a separation roller stretching the transfer belt and the stiffness of the recording material. In other words, the recording material is kept stuck to the transfer belt at the position of the separation roller to cause a separation defect. Japanese Patent Application Laid-Open No. 09-015987 discusses a method for separating the recording material such that protrusions are uniformly formed on the separation roller stretching the transfer belt to provide a corrugation for the transfer belt at a separation position. The use of such a configuration allows the corrugation to be formed on the transfer belt at the separation position, however, the transfer belt is always caused to exert great tension locally. This causes local wear on the transfer belt, thereby irregularity in resistance affects transferability.
Japanese Patent Application Laid-Open No. 05-119636 discusses a method for decreasing wear due to deformation while deforming the sheet carrying the recording material to separate the recording material. Japanese Patent Application Laid-Open No. 05-119636 also discusses a configuration in which a roller is provided as a boosting unit which can move to positions where the transfer sheet is boosted from the inside and not boosted. In the method discussed in Japanese Patent Application Laid-Open No. 05-119636, the roller boosts the transfer sheet to separate the recording material. The transfer sheet is not boosted while the recording material is not separated.